In this chapter we have presented an object-oriented metamodel for content processing and transmission (OOCTM). This metamodel may be seen both as an extension and a particularization of the Digital Signal Processing Object-Oriented Metamodel presented in chapter 4 and presents a way of modeling signal processing applications that deal with all aspects of content-based processing such as content analysis or content-based transformations.
The metamodel is based on two conceptual foundations: on one hand we call content to any semantic information that is meaningful for the target user; on the other hand, and applying one of the object-oriented paradigm maximas, we state that all semantic information contained in a given signal can be modelled as a collection of related objects.
Following the traditional Shannon&Weaver model for information transmission our metamodel is divided into three main components: a semantic transmitter, a channel, and a semantic receiver. The semantic transmitter is in charge of performing a multilevel analysis on the signal, identifying objects and finally building a multilevel object-based content description and encoding it in an appropriate format such as XML. The channel transports this metadata description and any added noise will not be considered as such unless the original meaning is modified. Finally the semantic receiver receives the multilevel content description, decodes it and translates it into a synthesizer-readable format. The synthesizer included in the receiver then synthesizes the output signal.
It is important to note that we are not so much interested in the fidelity of the final synthesized signal to the original but rather on whether the original ``meaning'' is preserved and is useful for the final user.
The Object-Oriented Content Transmission Metamodel can be seen as an extension of the classical Shannon&Weaver model for information transmission. The metamodel should be understood as a conceptual framework that can be instantiated to build working applications. In this sense it demonstrates how new technological advances have brought up the opportunity of redefining a communication model that is more than 50 years old. The metamodel is very much related to the Structured Audio metamodel and can also be seen as a step beyond parametric encoding. Finally if we add a transformation function to the channel we end-up having a general scheme for content-based transformations.
Anyway one may question the benefits of content-based audio applications. It is our opinion that by concentrating on the transmission of content description we are actually favoring the distinction between content and its realization. And, by doing so we favor a higher level approach, encapsulation, concept reuse, the upcoming of new applications (i.e. content-based transformations), data reduction, and robustness enhancement, to name a few. In this sense in the current chapter we have also given several examples of applications that represent particular instances of the metamodel or subparts and one in particular that instantiates the whole metamodel in order to transmit and synthesize a previously analyzed and extracted musical melody.
As a conclusion we may state that we have presented a new metamodel for information transmission that does care about meaning and content. The Object-Oriented Content Transmission uses a fully object-oriented view and an interpretation of content as any meaningful information for the user in order to present a conceptual framework that can give rise to many new and interesting applications. We have shown in practice some sample applications and, although still embrionary, they demonstrate the practicality of the metamodel.